Pesticides in the Atmosphere of the Mississippi River Valley, Part II - Air

ABSTRACT

Weekly composite air samples were collected from early April through mid-September
1995 at three paired urban and agricultural sites along the Mississippi River
region of the Midwestern United States. The paired sampling sites were located
in Mississippi, Iowa, and Minnesota. A background site, removed from dense urban
and agricultural areas, was on the shore of Lake Superior in Michigan. Each
sample was analyzed for 49 compounds; of these, 21 of 26 herbicides, 13 of 19
insecticides, and 4 of 4 related transformation products were detected during
the study, with most pesticides detected in more than one sample. The maximum
number of pesticides detected in an air sample was 18; this sample was from
the Iowa City urban site in mid-June. Herbicides were the predominant type of
pesticide detected at every site. The detection frequencies of most herbicides
generally were comparable at the paired Iowa and Minnesota sites. In Mississippi,
herbicides generally were detected more frequently at the agricultural site.
The insecticides chlorpyrifos, diazinon, and carbaryl, which are used in agricultural
and nonagricultural setttings, were detected more frequently in urban sites
than agricultural sites in Mississippi and Iowa. Methyl parathion was detected
in 70 percent of the samples from Rolling Fork, Miss., and at the highest concentration
(62 nanograms per cubic meter of air) of any insecticide measured in the study.
At the background site, dacthal (100 percent), atrazine (35 percent), cyanazine
(22 percent), and the (primarily atrazine) triazine transformation products
CIAT (35 percent) and CEAT (17 percent) were detected most frequently, suggesting
their potential for long-range atmospheric transport. Estimates of the pesticides'
particle and gas distribution provided insight into the primary mechanisms of
pesticide transport and deposition.